在高功率密度激光束的加热下。δ0．5mm～δ6mm板材的表面温度会迅速升至沸点温度。部 分材料汽化成蒸汽消失．部分材料作为喷出物从切缝底部被辅助气流吹走。切割气体一般用氮气(N2)或氩气(Ar)。常用空气或氮气作为辅助气体，每个脉冲 激光只产生小的微粒喷 射。逐步深入，因此厚板穿孔时间需要几秒钟。一旦穿孔完成，立即将辅助气体换成氧气进行切割。
当入射的激光束功率密度超过某一值后．光束照射点处材料内部开始蒸发，形成孔洞。它将作为黑体吸收所有的入射光束能量。小孔被熔化物质所包围。然后．与光束 同轴的辅助气流把孔洞周围的熔融材料带走。随着工件移动，小孔按切割方向同步横移形成一条切缝。 切割气体一般用氮气(N2)。
对于δ0．5mm~6mm的同一种料厚的板料，单位时间内从喷嘴喷出氮气气体体积随着使用压力的提高而提高，对于不同料厚的板料．在同一压力下单位时间内 从喷嘴喷出气体体积增量与料厚增量的平方成正比。由于氮气压力在6bar以上才对切割起到有效作用。所以气 体消耗量大。
对于δ0．5mm~δ6mm厚的板材．大多数热切割技术都必须在板上穿一小孔。激光冲压复合机上是用冲头先冲出一孔。然后再用激光从小孔处开始切割。对于 没有冲压装置的激光切割机一般用脉冲穿孔的基本方法--脉冲穿孔：金属对10．6um激光束的起始吸收率只有0 ．5％~10％。当功率密度超过 106W／cm2的聚焦激光束照射到金属表面时。却能在微秒级的时间内很快使表面开始熔化。
Laser cutting machine for stainless steel sheet metal processing is an advanced processing method which develops rapidly and is applied more and more widely. Since 90s, because of the development of China's socialist market economy and the fierce competition among enterprises, every enterprise must choose some advanced manufacturing technology correctly to improve the quality of product and production efficiency according to its own conditions. Therefore, laser cutting technology has gained rapid development in China.
The main process of laser cutting of stainless steel sheet metal is:
(1) sublimation and cutting
Under the heating of a high power density laser beam. The surface temperature of the delta 0.5mm to 6mm plate will rapidly rise to the boiling point temperature. Some of the material is vaporized into vapour. Some of the material is blown away from the bottom of the slit by auxiliary airflow as ejecta. Nitrogen (N2) or argon (Ar) is usually used for cutting gas. When air or nitrogen is used as auxiliary gas, each pulse laser produces only small particles. Gradually, the time required for thick plate perforation takes several seconds. Once the perforation is completed, the auxiliary gas is changed into oxygen for cutting.
(2) flame oxidation and melted cutting
Melt cutting usually uses inert gases, if replaced by oxygen or other reactive gases. The material produces another heat source under the irradiation of the laser beam and the intense chemical reaction with oxygen. It is called oxidation and melting cutting. Gas is usually used for cutting gas (02).
(3) high pressure gas focusing and melting cutting
When the power density of the incident laser beam exceeds a certain value, the material inside the beam point begins to evaporate and form a hole. It will absorb all incident beam energy as a blackbody. The small holes are surrounded by molten material. Then, the auxiliary air stream coaxial with the beam takes away the molten material around the hole. As the workpiece moves, the hole moves along the direction of cutting to form a slit. Nitrogen is usually used for cutting gas (N2).
For the same material of the same thickness of the delta 0.5mm~6mm, the volume of nitrogen gas from the nozzle in unit time increases with the increase of the use pressure. For the plate with different material thickness, the Ping Fangcheng positive ratio of the volume increment of the gas and the increment of the thickness of the material is sprayed from the nozzle under the same pressure. Because nitrogen pressure is above 6bar, it plays an effective role in cutting. So the gas consumption is big.
For plates with a thickness of delta 0.5mm~ 6mm, most heat cutting techniques must wear a small hole on the board. Punch is used to punch out a hole first. Then the cutting begins with a laser from a small hole. For the laser cutting machine without punching device, the basic method of pulse perforation is pulse perforation: the initial absorption rate of the metal to the 10.6um laser beam is only 0.5%~10%. When the power density exceeds 106W / cm2, the focused laser beam irradiates the metal surface. But it can quickly melt the surface at microsecond time.
Stainless steel sheet metal processing laser cutting machine analysis of gases in different materials
Structural steel, which is cut by oxygen, will get better results. When oxygen is used as the processing gas, the edge of the cutting will be slightly oxidized. For plates with a thickness of 4mm, nitrogen can be used as cutting gas for high pressure cutting. In this case, the cutting edge will not be oxidized. The plate with a thickness of more than 10mm will produce better results for the use of special plates in the laser and oil coating on the surface of the workpiece.
Stainless steel, cutting stainless steel needs to use oxygen, when the edge oxidation is not important, the use of nitrogen to get no oxidation without burr edge, no need to be treated again. Coating the oil film on the surface of the sheet will achieve better perforation effect without decreasing the machining quality.
Aluminum, despite its high reflectivity and thermal conductivity, can cut aluminum material below 6mm thickness, depending on the type of alloy and laser power. When cutting with oxygen, the cutting surface is rough and hard. When nitrogen is used, the cutting surface is smooth. Pure aluminum is very difficult to cut because of its high purity. Only when the system has a reflective absorption device can the aluminum material be cut. Otherwise the reflection will destroy the optical component.
Titanium and titanium plates are cut by argon and nitrogen as processing gas. Other parameters may be referred to as nickel chromium steel.
Copper and brass, two kinds of materials all have high reflectivity and very good thermal conductivity. The thickness of the laser cutting machine is less than 1mm, and the brass can be cut by nitrogen. The copper below 2mm thickness can be cut, and the processing gas must be used with oxygen. Copper and brass can only be cut off when the system has a reflective absorption device installed on the system. Otherwise the reflection will destroy the optical component.
Working principle of stainless steel sheet metal processing
Laser cutting machine makes full use of laser beam to process raw materials. By laser, raw materials can be melted, vaporized, broken and so on. After the material absorbs laser energy, the material will be cut off. At present, most of the use is carbon dioxide laser source, working power from several hundred watts to thousands of watts, but compared to comparison, it is a relatively low power value. After specular reflection, the laser beam will be highly concentrated, and finally the material will melt. At present, in China's industrial field, laser cutting machine is the most widely used.
Advantages of stainless steel sheet metal processing
Compared with other cutting machines, laser cutting machines have many advantages.
1, the quality of material cutting is better than that of other cutting machines. The material cut out is narrow, which saves raw materials to a great extent.
2, the cutting surface after cutting is neat and smooth, and does not need to be cleaned and cleaned step by step in the later period. It can be directly applied to the final molding and welding of the parts. Moreover, the force distribution is very uniform, and the material will not change after cutting.
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